1. Field of the Invention
The present invention elates to a hydraulic valve lifter having function to stop valve drive and more particularly to a hydraulic valve lifter having function to stop valve drive for an engine.
2. Description of the Related Art
A conventional hydraulic valve lifter having function to stop valve drive 73 for an engine shown in FIG. 2, is disclosed in Japanese Patent Laid-open No. 61(1986)-11411. Here, a hydraulic valve lifter 71 is located in a cylinder 72 formed in an engine block 73. A lifter body 74 contacts with an outer surface of a cam 75 and a tappet 76 contacts with one end of a valve stem 77. A ring 84 prevents the tappet 76 from falling out from the lifter body 74. A valve spring 78 is interposed between a retainer 79 fixed to the valve stem 77 and a retainer 80 located on a bottom of the cylinder 72.
A room formed between the lifter body 74 and the tappet 76 is divided into a reservoir 81 and a pressure room 82 by a plunger 83. The reservoir 81 is in fluid communication with a hydraulic source 85 via a hydraulic line 86 and through holes 87,88. The pressure room 82 is in fluid communication with the reservoir 81 via an orifice 89. The orifice 89 is opened and closed by a check valve 90. A spring 91 is interposed between the tappet 76 and the plunger 83 and urges the tappet 76 downwardly.
A piston 92 having a rod 93 si located in a cylinder 94 and is urged upwardly by a spring 95. A pressure room 96 formed in the lifter body 74 is in fluid communication with the hydraulic source 85 via a hydraulic line 97, valve 98 controlled by controller 100 and through hole 99.
In the above mentioned hydraulic valve lifter 71, when the valve 98 is closed, a pressure in the pressure room 96 is low. So the rod 93 parts from the check valve 98, and the pressure room 82 has been kept in high pressure condition by being supplied with the hydraulic pressure from the hydraulic source 85. Thus, a rotating torque of the cam 75 is transmitted to a valve 101 via the lifter body 74, plunger 83, the pressure room 82 having a rigidity by the hydraulic pressure therein and tappet 76.
On the other hand, if a vertical motion of the valve 101 is not needed, the controller 100 controls the valve 98 in the opening condition. So, the pressure room 96 becomes in high pressure condition, and the rod 93 presses the check valve 90 via the piston 92. Thus, the pressure room 82 is in fluid communication with the reservoir 81 via the orifice 89, and the rigidity of the pressure room 82 disappears. As a result, the rotating torque of the cam 75 is not transmitted to the valve 101.
Here, the hydraulic pressure in the reservoir 81 urges the piston upwardly. So, when the hydraulic pressure is supplied to the pressure room 96, moving responses of the piston 92 and rod 93 is bad. Thus, the vertical motion of the valve 101 dose not stop immediately, when it is not needed.